National Salmon Monitoring Programme

Conservation Limits have been set for all 148 Irish salmon rivers and recreational and commercial inshore fisheries are now regulated relative to these conservation limits being met on a river by river basis. The Standing Scientific Committee (SSC) of IFI annually reviews all data for salmon rivers to provide scientific advice on the compliance levels (i.e. CL attainment levels). About twenty five rivers have fish counters and the upstream salmon run can be assessed against the number of salmon required to spawn (the Conservation Limit) and this allows the scientists to give advice on the salmon surplus that can be taken each year, either by anglers or draft net fishermen. There are a further forty rivers where recent rod catches enable an estimate of the total returning stock to be made as anglers on average exploit about 15% of the available salmon stock. Therefore, there are 65 rivers with a direct measure of adult salmon abundance where the attainment of salmon conservation limits can be assessed nationally.

Many rivers have no direct means of assessing attainment of conservation limits and the assessments described below allow an assessment of attainment of CL to be undertaken.

Indirect measures of assessment

Prior to the 2010 salmon season the scientific advice identified 35 rivers under CL and therefore there were no harvest options available to allow a fishery to take place. Most of these rivers do not have a fish counter and there was no rod catch made in 2010 to allow for estimation of upstream escapement. Therefore there was no direct measure of salmon runs to advice on stock status for future years. No assessment of CL attainment can be made for the another forty five salmon rivers (mainly small systems) as they do not have counters or very low rod catches (< 10 per annum) are recorded and these rivers have been closed to angling exploitation.

It will not be possible to install fish counters in all rivers to assess stock status and many rivers will remain closed in the future unless other measures of stock strength can be found. A number of indirect measures of salmon abundance have been identified including redd counts and juvenile salmon indices that can be used in the absence of direct measures.

Salmon Redd Counts

A national database of salmon redd counts, undertaken by IFI staff in each RBD, has been compiled to provide an indirect measure of annual abundance. The ability to count salmon redds varies from river to river depending on topography, river flow and catchment size, the spaty nature of catchments, etc. Even with rivers where good annual redd counts are possible, severe winter floods can hamper accurate data collection on a consistent annual basis. Redd count data is being used, where robust data exists, to provide an index of salmon abundance that can be used to advice on attainment of salmon conservation limits.

Juvenile Salmon Index

The abundance of salmon fry close to salmon redds in riffle areas has been used previously (Kennedy & Crozier, 1991) as an index of salmon abundance on the River Bush in Northern Ireland. This technique is now being developed for Irish salmon rivers to provide an index of juvenile salmon abundance on a catchment-wide basis. Catchment-wide electro-fishing was undertaken at 1092 sites in 40 catchments in 2010 to assess abundance and distribution of salmon fry. In total, 82 individual catchments have been surveyed in the first four years of this assessment.

Findings from the first three year of the programme were presented to the Standing Scientific Committee (2009), and, following statistical analysis, the SCC proposed that rivers which were predicted not to have a salmon surplus in 2010, but where the salmon fry index was ≥ 17, could be considered for catch and release in 2010. On this basis, the SSC proposed the opening of 8 rivers on a catch and release basis in 2010. The SSC proposed opening five rivers (Boyne, Bride, Glyde, Slaney and Milltown) in 2011 based on the 2010 catchment wide electro-fishing programme.

The technique has good potential for salmon stock assessment and is likely to be more reflective of salmon stock status in rivers where rod catch could not be used to estimate salmon stock size (i.e where limited angling occurs or in smaller rivers). Several years of data will be required to compile a robust dataset against which individual catchment performance and trends can be assessed. Catchment-wide electro-fishing is also important in providing managers with information on the distribution and abundance of salmon fry. The absence or low density of salmon fry may be related to water quality issues, obstructions, or habitat damage and areas of low abundance can be investigated.

The use of PIT tag technology to estimate total salmon runs at partial counter locations.

Several existing fish counters are partial counters, i.e. they only cover a portion of the river and only count part of the salmon run. Examples include the Slaney, Blackwater, Bandon, Corrib, and Moy where counters are usually located at the head of fish passes or traps. The recorded count on these rivers has to be raised by a factor to provide an estimate of the total upstream run. A project is being undertaken to improve the accuracy of the raising factor applied to these counts using PIT tag technology for assessing the efficiency of all partial counters.

Site specific studies are ongoing on the Boyne and Munster Blackwater counters to determine the accuracy of the current raising factor. Using PIT (Passive Integrated Transponder) technology adult salmon were PIT tagged in both systems in 2010, in co-operation with fishery owners, anglers and commercial fishermen. Pit-tags are small microchips (about the size of a grain of rice) which are mounted on plastic floy tags and attached to a sample of rod or net caught adult salmon. Each tag has a unique code. The proportion of these tagged fish passing through or over the customised PIT counting facilities at both sites will provide an estimate of the proportion of fish being counted at each partial counter.

Pit tagging needs to be undertaken over a range of water heights as the usage of a fish pass and counter may change with changing river flow conditions. However the technique has the ability to more accurately estimate total salmon runs at partial salmon count sites. The results of this research will provide a more accurate assessment of the proportion of the salmon run using fish counters and help derive total salmon runs at partial counter sites.

Further Information (contact details)

Dr. Patrick Gargan / Dr. William Roche Email: This email address is being protected from spambots. You need JavaScript enabled to view it.This email address is being protected from spambots. You need JavaScript enabled to view it.